The objective of this project was to evaluate the antioxidant activity of 3-dehydroshikimic acid (DHS) which could be used as a safe, naturally occurring antioxidant in processed foods. DHS is produced from 3-dehydroquinate through the action of 3-dehydroquinase in aromatic amino acid synthesis by bacteria. DHS was evaluated for antioxidant activity in a bulk oil, in liposomes suspended in an aqueous medium, and in a corn oil in water emulsion. DHS showed antioxidant activity comparable to that of butylated hydroxytoluene (BHT) or tertiary butylhydroquinone (TBHQ) in the bulk oil medium, but showed little activity in the other two assays. To define the mechanistic basis for this difference in activity, the oxidation products of DHS in these experimental systems were identified and quantified using GC/MS. Two major oxidation products, gallic acid and protocatechuic acid, were identified from the oil suspension containing DHS. Both of these compounds significantly suppressed oxidation of oil under the same assay conditions. At 48 hours of incubation, protocatechuic acid was the major component in oil, representing 66% of the total antioxidant fraction whereas DHS and gallic acid were present at 28% and 6%, respectively. DHS remained intact in the liposomal system throughout the assay period. Smaller amounts of gallic acid were observed in the corn oil emulsion upon oxidation, but protocatechuic acid was not detected. These results suggest that the superiority of DHS as an antioxidant in oils is the result of its ability to undergo conversion in lipid systems to protocatechuic acid and gallic acid which may act synergistically.